1. Field of the Invention
The present invention is directed generally to a slip clutch, and more particularly, to a clutch apparatus which disposes one or more spherical balls in grooves formed in the inner and outer cylindrical surface of concentrically disposed rotatable members.
2. Description of the prior art
Many types of slip clutches are known to those skilled in the art. In certain types of these applications, spherical balls are disposed in grooves that are shaped in generally flat radial surfaces of clutch members. For example, an overload clutch is described in U.S. Pat. No. 4,294,340 which issued to Kunze on Oct. 13, 1981. It discloses a clutch that includes a driving member, a driven member and clutch engagement members that are rotatably held in apertures formed in either the driving or driven member with recesses formed in the other member. The clutch engagement members engage to effect clutch torque transmission and the clutch is structured to include a control ring having recesses formed therein. The control ring is held by a circumferential spring in a first position and enables the clutch to be moved to a second position which represents a disengaged position.
U.S. Pat. No. 4,075,873 which issued to Geisthoff on Feb. 28, 1978 describes a free-wheeling overload coupling apparatus in which first and second coupling members are rotatable relative to each other. These coupling members are fixed axially with respect to each other with a third coupling member rotatably disposed between them. It disposes a plurality of torque transmitting balls circumferentially spaced in one of the members and spring biased axially toward the other member. The overload coupling described in the Geisthoff patent causes a disengagement between its components when an overtorque condition exists. This disengagement is reset manually for future operation.
U.S. Pat. No. 3,205,985 which issued to Pearl on Sept. 14, 1965 discloses a torque responsive clutch for use in association with power tools wherein the clutch is disengaged in response to a predetermined torque and remains disengaged until it is automatically reset through normal operation of the tool. The Pearl patent describes a torque responsive clutch which disposes a plurality of cylinders between inner and outer tapered bores. The inner bore comprises a plurality of lobes which, upon an overtorque condition, cause the cylinders to move radially outward toward the outer tapered bore. The outer member is deformable and permits the cylinders to pass over the lobes which provides the slippage between the driving and driven members.
Clutches of the type described above typically utilize frictional forces between driving and driven members to transmit torque therebetween. When sliding friction is used in this way by a clutch apparatus, accurate setting of the break away torque value is difficult because of the inherent variability that is typical in friction devices. The coefficient of friction between clutch members can vary by significant amounts and this variability adversely affects the precision with which the actuation torque of the slip clutch can be set.